Sound reproducer



Jan. 14, 1936 E. W. FRANCK SOUND REPRODUCER Filed June 28, 195

IN V EN TOR. Ewes! h/fianc/n,

Patented Jan. 14, 1936 STATES PATENT OFFICE A Claims.

This invention relates to new and useful improvements in soundreproducing means and has particular relation to a means for reproducingsound from phonograph records.

Amongst its other objects the invention aims to provide a reproducerwhich is of simple and economical construction whereby it may beproduced at low cost, and which will give a clear and loud reproductionof a record, and which may be light in weight.

Another object of the invention is to provide a sound reproducer whichis completely self-contained and which is not dependent on the use ofany horn or other air-column as a portion of its dampening means.

Other objects and advantages will become apparent from a considerationof the following detailed description taken in. connection with theaccompanying drawing wherein a satisfactory embodiment of the inventionis shown. However, it will be understood that the invention is notlimited to the details disclosed but includes all such variations andmodifications as fall within the spirit of the invention and the scopeof the appended claims.

In the drawing:

Fig. 1 is a top plan view of the reproducer;

Fig. 2 is a bottom plan view thereof;

Fig. 3 is an edge view looking from the lower side of Fig. 1;

Fig. 4 is a sectional view taken substantially along the line 4-4 ofFig. 1;

Fig. 5 is a perspective view showing a slightly modified form ofdiaphragm stretching means employed;

Fig. 6 is a similar view showing a further modified form of said means;

Fig. 7 is a perspective view of a stylus holder; and

Fig. 8 is a detail sectional view showing a slight modification ofdiaphragm.

In the drawing, my improved reproducer is generally designated Ill andas shown comprises a diaphragm supporting means H in the form of anannulus. A diaphragm disc I2 has its edge portion secured in anysuitable manner to the supporting ring or annulus I I and as shown thesaid diaphragm is of celluloid although any other suitable material maybe used. Against any selected portion of one side of the disc I2 thereis secured, as by a suitable adhesive, a plate I3 of relatively thinwood. If desired, the plate I3 may be of material other than wood as,for example, it may be of relatively still celluloid or any othermaterial which will stiffen the portion of disc I2 to establish a pistonmotion when oscillating forces are applied to it by means of a stylus aswill later appear.

To the side of the diaphragm opposite the plate I3 there is secured astylus holder gener- 5 ally designated I4 and which may be bent up fromsheet metal. This stylus holder includes base portions I6 and portionsI1 and I8 extending at right angles to the base portions It. The baseportions I6 are suitably secured as by ce- 1() ment or glue to thecentral portion of the disc I2 and a stylus I9 is held between theportions I! and I8 of the holder. The said stylus is mounted byinserting its blunt end between the holder portions I1 and I8 and thenpinching or 15 squeezing said portions together against the stylus. Ifdesired, a drop of adhesive may be used to further secure the stylus inplace and to secure the holder portions .I1 and I8 together.

In the manufacture of the improved repro- 2 ducer the plate I3 may besecured to the central portion of the celluloid disc I2 and thereafterthe holder I4 containing the stylus I9 may be secured to either side ofthe diaphragm. This subassembly may then be secured to the supportingring II by cementing or clamping the edge of the celluloid disc ordiaphragm to one edge of said ring, it being understood that suchsub-as- .sembly constitutes a diaphragm with a stiifened or non-flexingcenter. If desired, the disc I2 :mayfirst be clamped. to the supportingring and thereafter the stiffening plate and stylus holder may besecured to the said disc.

In mounting the disc I2 on its support it is desirable to follow amethod whereby all wrinkles are removed from the disc. Thereafter, thethin celluloid disc I2 is tensioned and this is accomplished by pressingthe free edges of the walls '20 of a shallow dish or dome shaped member2| against one side of said disc. In addition to the 40 ring-like wall20 the member 2I includes a closed outer wall 22 having a raised rib orbead 23 extending partly across the same and through its centralportion. The member 2I is held against the disc I2 by means of a springclip 24 here shown as comprising a wire or rod extending across thesupport II and having its end portions bent downwardly and. xtheninwardly as at 25 so as to engage against the lower edge of said support.I I. Intermediate its ends the clip 24 is pressed upwardly as at 26 toprovide a slight notch in its lower side. This notch receives a portionof the rib .23 whereby to locate the member 2| in the desired positionwith respect to the support II and the disc I2 to further locate clip 24the support 2 may becrimped at diametrically opposite points I 2a toreceive the arms of the clip.

It will be understood that the clip 24 being resilient or springy,presses the member 2| against the celluloid disc I 2 whereby the latteris tensioned and its central portion within the wall 20 of the member 2|is in a flat stretched condition and of a diameter desired and in theoperation of the diaphragm in the reproduction of a record thisstretched central portion covered by disc l3 acts as a piston in thereproduction of vertically cut or hill-and-dale records. When the member2| is not in place a very poor or low volume and indistinct reproductionmay be obtained from a record. However, with the member 2| in place aloud metallic reproduction results and to overcome this I insert adamper 21 in a form of a piece of felt or the like into the member 2|.

This means 21 is of compressible material and normally is of a thicknessgreater than the depth of the member 2| whereby when it is in saidmember and the member is clamped against the disc |2 the said damper isslightly compressed and is held against one side of the diaphragm. Withmeans 21 in place highly satisfactory reproduction of the desired volumeand clarity is obtained. However, the damping means may be other thanthat shown and may be in the form of a sheet of suitable materialsecured to the diaphragm by adhesive or may be held in place by aspring. Also, if desired the damping means may be applied to thediaphragm at the side thereof opposite to that on which the member 2| islocated.

When the device is used for the reproduction of lateral cut records asdistinguished from hilland-dale records the line or bend 28 of thestylus support l4 represents-a fulcrum to change the direction of theforce of the lateral vibrations acting through the stylus with theresult that the portions of the diaphragm at opposite sides of this lineare rocked vertically in opposite directions as the stylus follows therecorded groove of the laterally cut record. To better adapt thereproducer for reproducing such records a shallow-cup-like member 29(see Fig. 5) should be substituted for the member 2| of Figs. 1 through4. This member 29 is in all respects similar to the member 2| with theexception that a partition 30 divides the interior of the member 29 intotwo parts or chambers and when the member 29 is in use its partition 3|]is aligned with the stylus l9 and is pressing against the diaphragm.

Fig. 6 shows a further modification of a tensioning and damping meansholder and in this figure the member generally designated 3| is ashallow cup-like member and differs from the member 2| previouslydescribed only in that the member 3| has an opening 32 through its outeror back wall portion 33. When the hole 32 is not overly largesatisfactory reproduction may be obtained when using a member as 3|.However, when the hole in the wall 33 is enlarged the quality and volumeof reproduction is impaired as the size of the hole increases.

In the design of reproducers of this type considerable control over theperformance may be exercised by varying the size and weight of thisplate l3. It will be readily seen that if this plate is increased indiameter or size so that its edges approach the wall 20 of disc 2| thenthe diaphragm stiffness is greatly increased. On the other hand, if thedisc is decreased in diameter or size, the diaphragm stiffness will begreatly decreased. Thus, by keeping all other dimensions constant, andvarying the size of this plate 3 the effective stiffness of thediaphragm may be changed. It is a well known fact that a stretcheddiaphragm with a mass disposed at its center or about its center willhave its own natural period of resonance. In general this resonancefrequency may be increased by the use of stiffer diaphragm material, byincreased stretch in the diaphragm, or, as I find it often convenient,by increasing the size of plate I3 as just explained.

The resonance frequency of a weighted and stretched diaphragm may alsobe controlled to a considerable extent by varying the mass of thecentral portion. Reducing this mass will result in an increasedresonance frequency, and increasing this mass will lower the resonancefrequency. In general I find it is advisable to keep the mass of thecentral portion reasonably small, d

and to control the resonance frequency to give the desired performanceby selecting the proper size for disc l3 and adjusting the amount ofstretch in the diaphragm.

Whenever a stretched diaphragm with central mass is agitated by avibromotive force whose frequency is near to the resonant frequency ofthe stretched diaphragm, there is a tendency for the amplitude of thediaphragm excursions to become excessive and cause a buzzing which isvery detrimental to the quality of reproduction. In the conventionalreproducer this tendency towards buzzing when excited at frequenciesclose to resonance is usually counteracted by the dampening efiectprovided by the air-column load of a horn, megaphone, or car tubes.Because of this effect, the ordinary type of reproducer is quiteunsatisfactory when it is not used in conjunction with its horn orair-column load. Certain types of electro-magnetic load-speakers havebeen made with a diaphragm having large area and large effective mass.The large effective mass of this type diaphragm, together with the lowstiffness of the material used resulted in very low resonance frequency.Besides having a relatively low resonance frequency, this typereproducer also has a large area so that a considerable air load iseffective as a dampener although there is no air-column as the term isgenerally used.

In my device, I control this tendency towards too great freedom at theresonance frequency without the use of the usual air-column load, andwithout resorting to a diaphragm of low stiffness and/or great area.Thenovel means I use will be understood by refeernce to Figs. 1 through4 and will be seen most clearly by reference to Fig. 4. Here is showndome-shaped member 2| with wall 26 held against one face of thediaphragm disc I2. It will be seen that with the damping material 21,held in engagement with one face of the diaphragm |2 as before describedthe entire area of the diaphragm within the wall 20 which is engaged bythe dampening material is effectively uniformly loaded in the sense thateach element of area of the diaphragm Within the wall 20 must actuallydo work on the damping material as it vibrates. I find that the bestdamping materials for use here are certain kinds of sponge rubber andcertain types of woolen fabric.

Fig. 8 shows a modified construction of means for stiffening the centralportion of the disc I 2 so as to have such portion function with apistonlike movement. In the figure a cone shaped sheet metal piece 34having a relatively large diameter flange 35 is secured to the disc 12.The flange is cemented or otherwise secured to the disc and stiffens thelatter and the cone has a stylus 36 secured thereto as shown.

In some forms of my invention I make use of still another form ofdamping, which, while usually not suflicient in itself to control thediaphragm at resonance, is of distinct benefit when used in combinationwith the method of diaphragm loading described immediately above. When aclosed member as M is employed and the free edge of its wall 28 ispressed tight against the disc 52 a seal is established and any movementof the diaphragm results in compression and expansion of the air in themember 2i and this constitutes a load on the diaphragm. This is true ofcourse only when the cup or member is shallow and closed at its back.

Having thus set forth the nature or" my invention, what I claim is:

1. In a sound reproducer, a supporting means, a diaphragm comprising asheet supported against said means, an annulus held tight against saidsheet to produce a plane radial tension in the diaphragm, a stylusholder connected with said diaphragm, and damping means engaging thediaphragm within said annulus.

2. In a sound reproducer, a supporting means, a diaphragm supported atits edges by said means, a shallow cup-like member disposed with itsopen side toward the diaphragm and with its free edge against thediaphragm, tensioning means pressing the free edge of said memberagainst the diaphragm to produce a plane radial tension in a centralportion thereof, a stylus holder connected with the diaphragm, anddamping means within said member against the diaphragm.

3. In a sound reproducer, a supporting means, a diaphragm supported atits edges by said means, a shallow metal cup-like member disposed withits open side toward the diaphragm and with its free edge against thediaphragm inwardly of said supporting means, tensioning means pressingthe free edge of said member against the diaphragm, a stylus holderconnected with the diaphragm, and damping means engaging the diaphragm.

4. In a sound reproducer, a supporting means, a diaphragm supported atits edges by said means, a shallow rigid cup-like member disposed withits open side toward the diaphragm and with its free edge against thediaphragm inwardly or" said supporting means, tensioning means pressingthe free edge of said member against the diaphragm, a stylus holdersecured to the diaphragm, and damping means within said member againstthe diaphragm.

5. In a sound reproducer, a supporting means, a diaphragm supported atits edges by said means, a shallow rigid cup-like member disposed withits open side toward the diaphragm and with its free edge against thediaphragm inwardly of said supporting means, a spring clip spanning saidsupporting means and having its intermediate portion pressing againstsaid member to press its free edge against the diaphragm and produce aplane radial tension in the latter, and a stylus holder connected withthe diaphragm.

6. In a sound reproducer, a supporting means, a diaphragm supported atits edges by said means, a shallow cup-like member disposed with itsopen side toward the diaphragm and with its free edge against thediaphragm inwardly of said supporting means, a spring clip spanning saidsupporting means and having its intermediate portion pressing againstsaid member to press its free edge against the diaphragm and produce aplane radial tension in the latter, a stylus holder connected with thediaphragm, and a damping means within said member and pressed againstthe diaphragm thereby.

7. In a sound reproducer, a supporting means, a diaphragm supported atits edges by said means, a shallow cup-like member disposed with itsopen side toward the diaphragm and with its free edge against thediaphragm inwardly of said supporting means, a rib on the outer surfaceof the back of said member, a spring clip spanning said supporting meansand clipped thereto and having a notch intermediate its ends receiving aportion of said rib to locate said member with respect to the diaphragm,said clip pressing the free edge of said member against the diaphragm toproduce a plane radial tension in the latter, and a stylus holderconnected with the diaphragm.

8. In a sound reproducer, a supporting means, a diaphragm supported atits edges by said means, a stifiening member secured to and concentricwith said diaphragm, a shallow rigid cup-like member disposed with itsopen side toward the diaphragm and with its free edge against thediaphragm inwardly of said supporting means, tensioning means pressingthe free edge of said member against the diaphragm to produce a planeradial tension in the latter, a stylus holder connected with thediaphragm, and damping means within said member against the diaphragm.

9. In a sound reproducer, a supporting means, a diaphragm supported atits edge by said means, a stifiening plate secured to the centralportion of the diaphragm at one side thereof, a sheet metal stylusholder connected with the central portion of said diaphragm andincluding a flat portion secured to the opposite side of said diaphragmand a pair of portions projecting outwardly of the diaphragm, and astylus secured between said outwardly projecting portions by beinggripped between them.

10. In a sound reproducer, a supporting means, a diaphragm supported atits edge by said means, a stiffening member secured to the centralportion of one side of the diaphragm, a sheet metal stylus holdersecured to the central portion of the other side of said diaphragm andincluding a fiat portion secured to said diaphragm and a pair ofportions projecting outwardly 01' the diaphragm, and a stylus securedbetween said outwardly projecting portions by being gripped betweenthem.

11. In a sound reproducer, a supporting means, a diaphragm supported bysaid means, an annulus, a spring clip holding said annulus tight againstsaid diaphragm in spaced relation to said supporting means to produce aplane radial tension in the diaphragm, and a stylus holder connectedwith said diaphragm.

12. In a sound reproducer, a supporting means, a diaphragm supported atits edges by said means, an annulus held tight against said diaphragm inspaced relation to said supporting means to produce a plane radialtension in the diaphragm, a stylus holder connected with said diaphragm,damping means, and means pressing said damp ing means against thediaphragm.

13. In a sound reproducer, a supporting means, a diaphragm supported atits edges by said means, a shallow rigid cup-like member disposed withits open side toward the diaphragm and with its free edge against thediaphragm inwardly of said supporting means, 'tensioning means pressingthe free edge of said member against the diaphragm and tensioning thelatter, a stylus holder connected with the diaphragm, damping means, andmeans pressing said damping means against the diaphragm.

14. In a sound reproducer, a supporting means, a diaphragm comprising asheet supported against said means, a rigid annulus held tight againstsaid sheet to tension the diaphragm, a stylus holder connected with saiddiaphragm, and a damper engaging the diaphragm within said annulus.

15. In a sound reproducer, a supporting means, a diaphragm supported bysaid means, an annulus having an edge against said diaphragm, a springclip spanning said supporting means and causing the edge of the annulusto press against the diaphragm and produce a plane radial tension in thelatter, and a stylus holder connected with the diaphragm.

16. In a sound reproducer, a supporting means, a diaphragm supported atits edges by said means, a shallow cup-like member disposed with itsopen side toward the diaphragm and with its free edge against thediaphragm inwardly of said supporting means, tensioning means pressingthe free edge of said member against the diaphragm and producing a planeradial tensioning of the latter, a stylus holder connected with thediaphragm, damping means, and said shallow cuplike member pressing saiddamping means against the diaphragm.

17. In a sound reproducer, a supporting means, a diaphragm supported bysaid means, a shallow rigid cup-like member completely closed at oneside and disposed with its open side toward the diaphragm and with itsfree edge against the diaphragm, tensioning means pressing the free edgeof said member against the diaphragm, and a stylus holder connected withthe diaphragm.

18. In a sound reproducer, a supporting means, a diaphragm supported bysaid means, a rigid member having an edge against said diaphragm, aspring clip spanning said supporting means and causing an edge of themember to press against the diaphragm and tension the latter, and astylus holder connected with the diaphragm.

19. In a sound reproducer, a supporting means, a diaphragm supported bysaid means, an annulus having an edge against said diaphragm, springmeans causing the edge of the annulus to press against the diaphragm andproduce a plane radial tension in the latter, and a stylus holderconnected with the diaphragm.

20. In a sound reproducer, a supporting means, a diaphragm supported bysaid means, a member having an edge against said diaphragm, spring meanscausing the edge of said member to press against the diaphragm andproduce a plane radial tension in it, and a stylus holder connected withthe diaphragm.

ERNEST W. FRANCK.

